<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS类选择器</title>
    <style>
        .red{
            color: red;
        }
        .size{
            font-size: 30px;
        }
    </style>
</head>
<body>
    <div class="red">div标签示例1</div>
    <div class="red size">div标签示例2</div>
</body>
</html>